1. Field of the Invention
The present invention relates to a joint mechanism used with robots, manipulators, etc., and more specifically to the joint mechanism for driving right and left upper arms and lower arms freely and independently in multi-directions.
2. Description of the Prior Art
In robots or manipulators, there are provided mechanisms for driving shoulder joints to move upper arms and mechanisms for driving elbow joints to move only lower arms. Actuators or motors included in these mechanisms are usually arranged concentratively at a position (called concentrated actuator arrangement system) or separately at some positions (called separated actuator arrangement system).
In the concentrated actuator arrangement system, the motors are concentratedly disposed on an appopriate position and one joint is driven by way of the other joints. Therefore, when the upper or lower arms are required to drive in predetermined directions, there exist problems in that plural joints should be driven simultaneously. That is, it is impossible to drive a joint independently without relation to other joints or without interference in movement between joints.
In the separated actuator arrangement system, since each motor is arranged at each joint, there exist problems in that it is rather difficult to keep balance of the arm in relation to the motor weight. Further, the balance weight is inevitably increased, thus causing an increase in dimensions or weight. In addition, another problem arises such that when the weight of the arm increases, it is necessary to increase the rigidity of the arms so that the arm can withstand acceleration or deceleration caused when moved quickly.
In addition, there exists another manipulator such that the shoulder joint is only pivoted and the drive shaft is arranged eccentrically with respect to the center line of the arm. In the manipulator of this type, since the rotational axis of the upper arm about the shoulder joint and the pivotal axis thereof in the back and forth direction are located at two different positions, it is difficult to manipulate or operate the manipulator by use of operation rods in the case of feedback control system.
In summary, it is ideal to construct and operate the manipulator joints as humanly as possible. In practice, the shoulder joint should be such that the pivotal axis of the arm is located on a straight line connecting the shoulder and the hand or fingers and the arm is pivoted about a horizontal pivotal axis perpendicular to the above straight line.
In the prior-art manipulators, it has been difficult to realize a humanized shoulder joint motion and a humanized elbow joint motion. In other words, there exists no manipulator easy for the operator to handle in accordance with human sense.